1. Field of the Invention
The present invention relates to a light-modulating material with a liquid crystal. A light-modulating material of the present invention is used as, for example, a front glass or a front side glass of a vehicle.
2. Description of Related Art
Penetration routs of light and heat into interior of a vehicle parked under burning sun in the summer season include a ceiling, a wind shield, a rear glass, a front side glass, a rear side glass, an upper part of doors, etc.
In many cases of the conventional vehicles, a laminated glass has been used as a wind shield, while a single glass as a front side glass. To enhance safety, an intermediate film may be used which contributes to improve strength, however, it has little thermal function. Therefore, high amount of light energy and heat energy penetrates into interior of a vehicle parked under burning sun, making interior vehicle environment very serious. It also reduces fuel economy of air conditioning equipment, which may provide bad effects on environment from macroscopic view point.
In building also, this problem has been studied. For example, by inflow of light energy and heat energy through windows, loads to air conditioning equipment in a room and a human body increase. Just like in a vehicle, inflow of high amount of energy worsens fuel economy of air conditioning equipment, which may provide bad effects on environment from macroscopic view point.
To solve these problems, such techniques have been proposed recently as to reduce temperature increase in a room and cooling load by shielding light energy and heat energy inflow into a building or a vehicle interior. As an example of such measures, a glass with light-modulating function is proposed. When both characteristics of transparency as a window glass and heat ray reflection/absorbability to shield direct sunlight energy, along with switching function as required are maintained, it is possible to introduce required amount of light into a room when needed. If such control is possible, it is useful to not only reduce load to a human body or cooling equipment but also in view of energy saving.
As specific measures to furnish light-modulating function to a glass, an electrochromic element (hereinafter called “an EC element”) and a liquid crystal element are known.
An EC element enables control of transmitting amount of direct sunlight energy via light absorption by using a material accompanying spectral changes by an electrochemical redox reaction such as tungsten oxide, prussian blue, etc. However, because of absorption of direct sunlight energy, an EC element, when it is used to a glass to partition interior and exterior of a room, energy thus absorbed is re-emissioned into a room, causing increase in room temperature.
A liquid crystal element is composed of a material with a function to change alignment by voltage, and change light perspectiveness by alignment of a liquid crystal. As a liquid crystal element, a nematic liquid crystal element with a curve-shaped aligned phase (JP-S58-501631), a liquid crystal element obtained by a phase separation method (JP-S61-502128), and the like are known. These elements work based on the following principle.
In an a liquid crystal element described in these gazettes, prepared by dispersion of small droplets of a liquid crystal substance into a cheap polymer, a liquid crystals align along a curved surface of a polymer wall in non-electrified state. By this effect, optical path is twisted and light reflects and scatters at interface between a polymer and liquid crystal droplets, and thus providing milky white color.
On the other hand, when voltage is impressed to a liquid crystal element, liquid crystals inside liquid crystal droplets align in the direction of electric field by external electric field. At this time, by selecting refractive index of a liquid crystal, no, and refractive index of a polymer, np, so that they are coincident, it is possible for incidented light vertically to a liquid crystal element surface to pass without reflection at interface between a liquid crystal and a polymer and thus makes a liquid crystal element transparent.